Not sure about the younger group, but I can see why it would, or rather to those after style and function - something, despite the colours and soft curves, the X series can't get away with.
Actually, the Felix came about when one of the original designers for Vorwerk ended up working at SEBO and designed a very similar model, obviously in conjunction with Vorwerk's previous design. Thus, the height adjustable handle comes from Vorwerk design as well as interchangeable floor heads and the swivel joint. Thus, the Felix was made for those looking for an upright in a medium home with the X designed for larger homes.
Evidently though it shares a similar bag capacity (by some 0.5 litres) to the K cylinder vacuum, the Felix has always had lower power to match the X4. That's excluding the 175 watt small PN or the 200 watt PN. I'd be interested to see if SEBO can lower the motor power of the PN with the EU law coming in.